import java.util.Stack;

public class MyStack {

    public int[] elem;
    public int usedSize;

    public MyStack() {
        elem = new int[10];
    }

    public void push(int val) {
        //1. 如果满了进行扩容
        
        //2. 才可以入栈
        elem[usedSize] = val;
        //3. us++
        usedSize++;
    }
}
